"Could not start the VM service" causing flaky DAP tests

[DanTup]

The DAP debug_test suite is often marked as flaky and sometimes times out after the output contains "Could not start the VM Service":

https://dart-ci.firebaseapp.com/#showLatestFailures=false&test=pkg/dds/test/dap/integration/debug_test

https://dart-ci.appspot.com/log/pkg-mac-release-arm64/unittest-asserts-release-mac-arm64/16673/pkg/dds/test/dap/integration/debug_test

00:14 �[32m+16�[0m�[33m ~1�[0m: debug mode runs with DDS by default�[0m
==> [DAP] {"seq":1,"type":"request","arguments":{"adapterID":"test"},"command":"initialize"}
==> [DAP] {"seq":2,"type":"request","arguments":{"filters":["None"]},"command":"setExceptionBreakpoints"}
==> [DAP] {"seq":3,"type":"request","arguments":{"breakpoints":[{"line":2}],"source":{"path":"/Volumes/Work/s/w/itzwa9nqnt/dart-sdk-dap-testgxf1DJ/appL4mffL/test_file.dart"}},"command":"setBreakpoints"}
==> [DAP] {"seq":4,"type":"request","arguments":{"sendLogsToClient":true,"program":"/Volumes/Work/s/w/itzwa9nqnt/dart-sdk-dap-testgxf1DJ/appL4mffL/test_file.dart"},"command":"launch"}
<== [DAP] {"seq":1,"type":"response","body":{"exceptionBreakpointFilters":[{"default":false,"filter":"All","label":"All Exceptions"},{"default":true,"filter":"Unhandled","label":"Uncaught Exceptions"}],"supportsANSIStyling":true,"supportsClipboardContext":true,"supportsConditionalBreakpoints":true,"supportsConfigurationDoneRequest":true,"supportsDelayedStackTraceLoading":true,"supportsEvaluateForHovers":true,"supportsLogPoints":true,"supportsRestartFrame":true,"supportsRestartRequest":false,"supportsTerminateRequest":true,"supportsValueFormattingOptions":true},"command":"initialize","request_seq":1,"success":true}
<== [DAP] {"seq":2,"type":"event","body":{},"event":"initialized"}
<== [DAP] {"seq":3,"type":"response","body":{},"command":"setExceptionBreakpoints","request_seq":2,"success":true}
==> [DAP] {"seq":5,"type":"request","arguments":{},"command":"configurationDone"}
<== [DAP] {"seq":4,"type":"response","body":{"breakpoints":[{"id":100000,"message":"Breakpoint has not yet been resolved","reason":"pending","verified":false}]},"command":"setBreakpoints","request_seq":3,"success":true}
<== [DAP] {"seq":5,"type":"response","command":"configurationDone","request_seq":5,"success":true}
<== [DAP] {"seq":6,"type":"response","command":"launch","request_seq":4,"success":true}
<== [DAP] {"seq":7,"type":"event","body":{"category":"stderr","output":"Could not start the VM service:\n"},"event":"output"}
<== [DAP] {"seq":8,"type":"event","body":{"category":"stderr","output":"\n"},"event":"output"}

I'm not sure if the message is being truncated (I think there should be more of the message afterwards?) - I'll try to determine this if I can find a way to repro.

@bkonyi the test itself is fairly simple (it just runs a Dart script in debug mode) so my feeling is that this may be something like failing to bind a port. Have you seen any other similar flakes in other tests along these lines that might be less cryptic?

[DanTup]

If I force a failure by forcing a port that's in use, like --enable-vm-service=135 then I do see a complete error when running this same test:

<== [DAP] {"seq":7,"type":"event","body":{"category":"stderr","output":"Could not start the VM service:\n"},"event":"output"}

<== [DAP] {"seq":8,"type":"event","body":{"category":"stderr","output":"DartDevelopmentServiceException: Failed to create server socket (An attempt was made to access a socket in a way forbidden by its access permissions.\r\n"},"event":"output"}

<== [DAP] {"seq":9,"type":"event","body":{"category":"stderr","output":"): 127.0.0.1:135\n"},"event":"output"}

So I wonder if the error being produces on the bots simply doesn't have any additional text?